This article is about bluescreen compositing, a special effects technique. For the Windows error message, see Blue screen of death.

Bluescreen is the film technique of shooting foreground action against an even-lighted blue background, which is then replaced by a separately shot "background plate" scene by optical composition.

Petro Vlahos was awarded an Academy Award for his development of bluescreen techniques. His technique exploits the fact that most objects in real-world scenes have a colour whose blue colour component is similar in intensity to their green colour component. Zbig Rybczynski also contributed to bluescreen technology.

Other colours are sometimes used instead of blue, including green ("greenscreen"), orange, or grey. The choice of colour depends on the subject. Blue is normally used for people because human skin has very little blue colour to it. The same is also true for green, so the director can choose which colour to use depending on makeup and costume. Orange screens are often used with model photography where the model contains both blue and green components. Screens that, at first sight, appear grey are occasionally used for digital compositing, although these are in fact coated with tiny half-silvered glass beads to give a significant degree of retroreflectivity (see retroreflector). A ring of coloured lights (usually LEDs) is placed around the camera lens, and the screen reflects this colour back to the camera. This technique reduces problems from performers casting shadows on the screen, and allows operation at low lighting levels. As the screen colour is defined by the colour of the ring light, it is easier to quickly change the screen colour, and to use a colour with a narrow range, making it easier to distinguish between the colour of the screen and colours on the subject. If the person being filmed wears clothing that is the same color as the screen, the computer will draw the background over the piece of clothing, which would make it look like the person had disappeared.

The television technique of chroma keying was originally developed as an inferior imitation of bluescreen. With modern digital compositing techniques, the two analog techniques have converged.

The bluescreen technique is used in moviemaking to combine footage of actors, objects and backgrounds that were shot separately. The background footage can be wholly or partially created using computer-generated imagery (CGI). In the early 2000s several movies were made, including , Sky Captain and the World of Tomorrow, Casshern, and Sin City that combined real actors shot against bluescreen with all-CGI backgrounds. Often actors played each scene separately to give the director greater freedom. Towards the end of 2004, Drew Carey hosted a TV show where comedians act against a greenscreen background with live audience interaction. After post-production, viewers watching the show would see animation interlaced with the live acting.

External links

• The Blue Screen / Chromakey Page
• Bluescreen LLC
• Ultimatte Corporation
• Reflecmedia